with the estimate \(\Gamma \equiv \Gamma _\text{PN} = 3/20\)  from PN theory. However, since we are going to apply the tapering close to the merger of the binary, where the PN approximation is not applicable, we treat \(\Gamma \)  as a phenomenological fudge factor and choose \(\Gamma = 1/50\) . The crucial input from PN theory is the functional dependence of \(\Delta {v}^\text{tape}\)  on \(\nu \) , \(v^{\rm {tape}}\)  and \(\mathcal {N}_{\rm GW}\) . The choice of the parameters \(f^{\text{tape}}_{22}\)  and \(\mathcal {N}_{\rm GW}\)  is completely phenomenological, and should be made to optimize the null test. Previous analyses on the LIGO-Virgo events reported in Refs. [1]}, [2]}, [3]}, [4]} used \(f^{\text{tape}}_{22} = 0.35 f_{22}^{\rm {peak}}\)  and \(\mathcal {N}_{\rm GW}=1\) . While we also employ these choices for the studies here, we devote Sec. REF  to investigate how results are effected when varying, in particular, the tapering frequency \(f^{\text{tape}}_{22}\) . Changing \(\mathcal {N}_{\rm GW}\)  in the range \(0.8\mbox{--}3\) , instead, does not affect the results significantly.
